l6 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



lime phosphate. These two parts may be easily sepa- 

 rated. If bone be thoroughly burned, the organic mat- 

 ter is consumed and the white lime phosphate remains, 

 retaining the form, the structure, and the stiffness of 

 the bone. On the other hand, if a bone be immersed in 

 a weak acid — HC1 — for several days, the lime phosphate 

 will be dissolved, leaving the organic tissue, also re- 

 taining the form and structure but not the stiffness of 

 the bone. It may now be tied in a knot. 



Structure. — Looking closely on the surface of bone 

 one can see with the naked eye long channels, and on 



Fl <5. 7- — Structure of bone : A, longitudinal ; B, cross-section ; A, Haver- 

 sian canals. 



cross-section pores like those seen in wood. In this re- 

 spect it differs from ivory, which has no such pores. 

 These are the Haversian canals (Fig. 7, /;). They are, in 

 fact, blood vessels of the bone. This is as much as can 

 be seen with the naked eye. Under the microscope, in 

 addition, we see that the bony matter is arranged in con- 

 centric circles or cylinders about the canals, and that 



